Crown ether functionalized substrates

ABSTRACT

A method for making crown ether functionalized substrates, which includes modifying crown ether-based molecules by reacting with carboxylic acid functionalize chains. The crown ether-based molecules are then attached to substrates, thereby forming crown ether functionalized substrates.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional patent application of Ser. No. 16/255,322 filed onJan. 23, 2019. The entire disclosure of patent application Ser. No.16/255,322 is incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention described herein may be manufactured and used by or forthe government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

BACKGROUND

Aqueous purification or decontamination methods vary depending on thecontaminants being removed from the aqueous solution. For example,purifying water from a river may include multiple steps where the waterhas to be chemically treated and filtered to produce drinkable water. Inaqueous decontamination methods, aqueous waste may be produced atindustrial facilities that requires the removal of specific contaminatesgenerated by that particular industrial production method. As a result,specific purification or decontamination methods are required to removeunique contaminants.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of examples of the present disclosure will beapparent by reference to the following detailed description anddrawings, in which like reference numerals correspond to similar, thoughperhaps not identical, components. Reference numerals or features havinga previously described function may or may not be described inconnection with other drawings in which they appear.

FIG. 1 is a flow diagram of an example of a method for making crownether functionalized substrates herein;

FIG. 2 is an example of a one-pot synthesis of crown etherfunctionalized molecules;

FIG. 3 is an example of a magnetite nanoparticle functionalized withcrown ether ligands;

FIG. 4 is a flow diagram of an example of a method for removing ioniccontaminants herein;

FIG. 5A-5B are ¹H NMR and ¹³C NMR spectra of a crown acid with thechemical shifts in parts-per-million (ppm) obtained using the methoddescribed herein;

FIG. 6A-6B are ¹H NMR and ¹³C NMR spectra of a bis-crown product withthe chemical shifts in parts-per-million (ppm) obtained using the methodherein;

FIG. 7 depicts powder X-ray diffraction results of magnetitenanoparticles, an example of crown ether functionalized nanoparticles,and another example of in-situ functionalized crown ether nanoparticles;

FIG. 8A-8B are Fourier-transform infrared spectroscopy (FTIR) results,with units of wavenumbers (cm⁻¹) (X-axis) vs. the absorbance (Y-axis)for bis-crown and crown acid obtained using the method herein;

FIG. 9 is an FTIR spectrum with units of wavenumbers (cm⁻¹) (X-axis) vs.the absorbance (Y-axis) for magnetite nanoparticles functionalized withcrown ether ligands via an in situ method described herein; and

FIG. 10A-10B are thermogravimetric analysis results showing thetemperature (° C.) (X-axis) vs. the weight (%) (Y-axis) for magnetitenanoparticles treated with crown acid and in-situ functionalizednanoparticles treated with crown acid.

DETAILED DESCRIPTION

Generally, aqueous purification or decontamination may be performed byusing techniques including forward or reverse osmosis, electrodialysis,or electrodeionization. These methods use fine pore membranes thatrequire high pressures. The membranes may malfunction or degrade overtime, which may require frequent replacement of the membranes. Othermethods of aqueous purification or decontamination, such asdistillation, require a large amount of energy or may be non-selectiveto remove all contaminants, which may be inefficient depending on thecontaminants being removed from an aqueous solution. Functionalizedmolecules, such as nanoparticles, have previously been prepared toselectively remove target analytes from different aqueous solutions.However, methods for producing these nanoparticles can be complex,multi-step processes.

In a method disclosed herein, a one-step procedure is described, whichproduces crown ether functionalized substrates. Crown etherfunctionalized substrates described herein can be prepared to targetspecific ionic contaminants in aqueous solutions. As a result, themethod disclosed herein to produce the crown ether functionalizedsubstrates is less complex and more efficient compared to othermultistep methods used to produce functionalized substrates to removetarget analytes. Furthermore, the crown ether functionalized substratescan be recycled by removing the ionic contaminants that are bonded tothe molecules on the substrates once the media is separated from themolecules. As such, the reversible method for removing ioniccontaminants described herein is a low cost, low energy method comparedto conventional methods of purifying or decontaminating aqueoussolutions.

In a first method disclosed herein, a method for making crown etherfunctionalized substrates is provided. The method includes modifyingcrown ether-based molecules, by reacting carboxylic acid functionalizedhydrocarbon chains with crown ether-based molecules, to produce modifiedcrown ether-based molecules. The modified crown ether-based moleculesare then attached to substrates, thereby forming crown etherfunctionalized substrates.

Referring now to FIG. 1, step 102 of method 100 includes modifying crownether-based molecules, where a carboxylic acid functionalizedhydrocarbon chain is reacted with crown ether-based molecules therebyforming modified crown ether-based molecules. In step 102, the reactionforms bifunctional crown ether-based molecules with a pendent carboxylicacid group in a single step. The carboxylic acid group allows themolecule to attach to a substrate through reaction or interaction withsurface hydroxyl groups or other functional groups on the substrate.This approach negates the need for protecting one of the carboxylic acidgroups, which avoids multistep methods for producing the multifunctionalcrown ether molecules.

Any aromatic crown-ether based molecule may be used and modified in thereaction. Some examples of crown ether-based molecules includesubstituted and non-substituted crown ethers containing an aromatic ringsystem, benzocrown ethers, azocrown ethers, metallacrown ethers,thiocrown ethers, cryptands, and combinations thereof.

The carboxylic acid functionalized hydrocarbon chains may be anystraight chain or branched chain that can generate a bifunctional crownether with a pendent carboxylic acid group. Some examples of the acidchains include a diacid chain, a polyacid chain, an aromatic acid chain,aliphatic acid chain, and combinations thereof. One specific exampleincludes any α,ω-dicarboxylic acid chain with about 4 to about 20carbons.

In another example, the dicarboxylic acid functionalized hydrocarbonchain is a bifunctional molecule that includes two terminal carboxylicacid groups. In another example, the two carboxylic acid groups arelocated anywhere on the acid chain. The carbon atoms in the dicarboxylicacid functionalized hydrocarbon chain may range from about 4 carbonatoms to about 100 carbon atoms. The crown ether-based molecules anddicarboxylic acid functionalized hydrocarbon chain may be present as asolution in a ratio of crown-ether based molecules to the dicarboxylicacid functionalized hydrocarbon chain ranging from about 1:1 to about1:10, respectively.

In step 102, in another example, the reaction between the dicarboxylicacid functionalized hydrocarbon chain and the crown either-basedmolecules occurs in the presence of an acid catalyst. Some examples ofthe acid catalyst include 7.7 wt % P₂O₅ in methanesulfonic acid (Eaton'sReagent), phosphoric acid, sulfuric acid, p-toluenesulfonic acid,heterogeneous acid catalysts (e.g., AMBERLYST®-15, NAFION®-H),heterogeneous Lewis acid catalysts, homogeneous Lewis acid catalysts,heterogeneous Brønsted acids, homogeneous Brønsted acids, andcombinations thereof. The reaction in the presence of an acid catalystmay occur for a time ranging from about 1 hour to about 48 hours. Thetemperature during the reaction may range from about 20° C. to about100° C.

FIG. 2 shows two examples of a crown acid synthesis. In one example, anα,ω-dicarboxylic acid chain is reacted with benzocrown ether in a 1:1ratio in the presence of Eaton's Reagent to produce bis-crown. In anexample, the α,ω-dicarboxylic acid chain is reacted with benzocrownether in a 1:3 ratio in the presence of Eaton's Reagent to produce crownacid.

Referring now to FIG. 1, the next step 104 of method 100 includesattaching the modified crown ether-based molecules to substrates,thereby forming crown ether functionalized substrates. Attaching thecrown ether-based molecules to a substrate may occur in-situ or throughpost-functionalization. Some examples of substrates include solid orporous particles (e.g., nanoparticles or micron sized particles), asolid or porous support, a solid or porous surface, and combinationsthereof.

In one example, the substrate is solid or porous particles arenanoparticles having a diameter ranging from about 1 nm to about 100 nm.In another example, the particles have a diameter ranging from about 100nm to about 1 micron. In a further example, the particles have adiameter ranging from about 1 micron to 500 microns. Some examples ofparticles that may be used herein include magnetic nanoparticles,superparamagnetic nanoparticles, and combinations thereof. The particlescan be metallic nanoparticles, metal oxide nanoparticles, and mixedmetal oxide particles. Some examples of metallic particles include:metals such as Fe, Co, Ni, Mn, lanthanides, and combinations thereof. Aspecific example of the magnetic particles is iron oxide nanoparticles,such as Fe₃O₄. FIG. 3 shows an example of a crown ether functionalizedmagnetite (Fe₃O₄) nanoparticle. Any superparamagnetic nanoparticle, suchas magnetite, may be used.

In another example, solid or porous supports may be used as thesubstrate. The solid or porous supports may be any solid or poroussupport that has surface groups that can react with the carboxylic acidgroup of the modified crown ether-based molecules or participate inanother interaction (e.g. hydrogen bonding). Some examples of materialsthat make up the solid or porous supports include metals, metal oxides,metalloid oxides, ceramics, polymers, and combinations thereof.

In another example, the substrate is a′solid or porous surface. Thesurface may be any solid or porous surface that has surface groups thatcan react with the carboxylic acid group of the modified crownether-based molecules or participate in another interaction (e.g.hydrogen bonding). Some examples of solid or porous surfaces includemetals, metal oxides, metalloid oxides, ceramics, polymers, andcombinations thereof.

The crown ether-based molecule may be attached to the substrate throughheating, mixing, sonication, refluxing, altering the pH of a solutionthat contains both the substrate and the crown ether ligand, andcombinations thereof. In one example, the crown ether-based molecule maybe attached to a particle during the particle formation (i.e., in-situ).For example, superparamagnetic nanoparticles may be prepared insolutions that also contain crown ether ligands. The solution may bemixed via sparging, and functionalized nanoparticles may be recovered bycentrifugation, and drying.

In another method herein, a method for removing ionic contaminants isprovided. The method includes mixing crown ether functionalizedsubstrates with media containing ionic contaminants, thereby binding theionic contaminants to the crown ether functionalized substrates,separating the crown ether functionalized substrates from the media, andregenerating the crown ether functionalized substrates.

Referring now to FIG. 4, step 402 of method 400 includes mixing crownether functionalized substrates with media containing ioniccontaminants, thereby binding the ionic contaminants to the crown etherfunctionalized substrates. In one example, mixing may include adding thecontaminated media to the crown ether functionalized substrates to forma mixture (e.g., adding a solution of the contaminated media to a solidsupport functionalized with crown ether-based molecules). In anotherexample, the crown ether functionalized substrates may be added to thecontaminated media to form a mixture (e.g., adding crown etherfunctionalized particles to the contaminated media in a solution).

In one example, the media includes seawater, aqueous waste streams, tapwater, municipal water supplies, brackish water, and recreational watersources (e.g., lakes and ponds). Some examples of the ionic contaminantsmay be sodium chloride from seawater, effluent waste from plating shops,painting shops, or cleaning operations, trace metals from any watersource, heavy metal ions (e.g., lead, mercury, cadmium, etc.), and toxicmetals (e.g., beryllium or chromium). In another example, the ioniccontaminant could be a particular ion of interest, such as a rareelement, that can be removed and later isolated.

In an example, the media may be mixed with the crown etherfunctionalized substrates using shaking, sparging, stirring, sonication,dynamic flow, or combinations thereof. In this method 400, the crownether functionalized substrates may be any of the crown etherfunctionalized substrates previously described herein in method 100. Inone example, the crown ether functionalized substrates are particles,such as magnetic particles, or superparamagnetic particles, that may beadded to a solution containing the media with a contaminant.

Referring now to FIG. 4, the step 404 of method 400 includes separatingthe crown ether functionalized substrates from the media. Any method ofseparation may be used to separate crown ether functionalizedsubstrates, that are bonded to ionic contaminants, from the media. Inone example, when the crown ether functionalized substrates are magneticor superparamagnetic particles with crown ether-based molecules bondedthereto, the particles may be separated from the media by applying amagnetic field. In another example, when the crown ether functionalizedsubstrates are a solid support or surface in a mixing chamber,separation may occur by removing the media from the mixing chamber. Inyet another example, when the crown ether functionalized substrate is asolid support, separation may occur by filtering the media through thesolid support.

Referring back to FIG. 4, step 406 of method 400 includes regeneratingthe crown ether functionalized substrates, thereby releasing the ioniccontaminants from the crown ether functionalized substrates. Someexamples of regenerating the crown ether functionalized substratesinclude chemical reduction or oxidation, electrochemical reduction oroxidation, exchange reactions, solvent washing, or combinations thereof.In an example, the chemical reduction or oxidation can be accomplishedby using a reducing or oxidizing agent. In another example, solventwashing can occur when two different solvents with significantlydifferent polarities are used to extract the contaminant ion from thecrown ether functionalized substrates.

After the crown ether functionalized substrates have been regenerated,the molecules can be dispersed back into contaminated media, havecontaminated media dispersed into a mixing chamber containing theregenerated crown ether functionalized substrates, or stored for lateruse.

To further illustrate the present disclosure, examples are given herein.It is to be understood that these examples are provided for illustrativepurposes and are not to be construed as limiting the scope of thepresent disclosure.

EXAMPLES

In all of the examples described herein, the syntheses were performed atambient temperature. Sample sonications were accomplished with a Branson3510 ultrasonic water bath. Fine particle-liquid separations werefacilitated using a Labnet/Hermle Z200A high capacity centrifuge.

Example 1: Synthesis of 12-oxo-12-(4′-benzo-15-crown-5-ether)-dodecanoicacid (Crown Acid)

First, Eaton's Reagent was prepared by adding P₂O₅ (24 g, 169 mmol) tomethanesulfonic acid (200 mL) and stirring the mixture at roomtemperature until the solids were completely dissolved. Dodecanedioicacid (5.1 g, 22.1 mmol) was then added to the Eaton's Reagent andstirred until completely dissolved. A solution of benzo-15-crown-5-ether(2.0 g, 7.45 mmol) in Eaton's Reagent (50 mL) was then prepared andadded drop-wise to the dodecanedioic solution over a period of 1.5 hoursat ambient temperature and allowed to react with stirring for anadditional 4.5 hours. The reaction mixture was then poured into 300 mLof chilled, deionized water to quench the reaction. The suspended solidswere separated by filtration and rinsed thoroughly with fresh deionizedwater. The solid was then extracted with approximately 300 mL of CHCl₃and filtered. The filtrate was placed in a separatory funnel andextracted with three, 200 mL aliquots of deionized water. The CHCl₃ wasdried with MgSO₄ and then removed under reduced pressure to yield 3.25 gof crude product as a waxy yellow solid (90% yield).

The crown acid was purified by dissolving 200 mg of crude product in 20mL of chloroform in a small beaker. An equivalent volume of heptane wasadded and the solution was heated to boiling until the volume wasreduced by half. The remaining hot heptane solution was decanted into aclean beaker and chilled in an ice bath for approximately 10 minutes to15 minutes to precipitate the product as a white solid. The solidproduct was collected by filtration and dried under reduced pressure(50% yield).

FIGS. 5A and 5B show ¹H NMR and ¹³C NMR spectra for crown acid. ¹H and¹³C NMR spectra were collected on a Bruker AC 300 MHz spectrometer inCDCl₃ and spectra were referenced to the residual solvent peaks (¹H, δ7.27; ¹³C, δ 77.16). FIG. 5A shows the ¹H NMR spectrum for the crownacid that was produced using the above method. The drawing insertassigns the protons to their corresponding NMR peak. Peaks 1 and 2represent the three aromatic protons with an integration of 2:1,respectively. This result confirms single addition of the dodecanedioicacid to the aromatic ring. Multiplets observed between 3.5 ppm and 4.5ppm represent the 16 protons in the crown ether moiety.

FIG. 5B shows the ¹³C NMR spectrum results for the crown acid that wasproduced using the above method. The ¹³C NMR reveals 26 peaks, which isalso consistent with the structure of12-oxo-12-(4′-benzo-15-crown-5-ether)-dodecanoic acid (i.e., crownacid). The peaks present at 199 ppm and 178 ppm are assigned as thecarbonyl carbons of the ketone and carboxylic acid groups, respectively.

Example 2: Isolation ofbis-1,12-[benzo-15-crown-5-ether]-2,11-dodecanedione (Bis-Crown)

For bis-crown, dodecanedioic acid (2.6 g, 11.3 mmol) was dissolved inEaton's reagent (100 mL) and stirred until completely dissolved.Benzo-15-crown-5-ether (3.0 g, 11.2 mmol) was added to the dodecanedioicacid solution at ambient temperature and allowed to react with stirringfor 6 hours. The reaction mixture was then poured into 100 mL ofchilled, deionized water to quench the reaction and allowed to cool. Thesolution was extracted with three, 100 mL aliquots of CH₂Cl₂. The CH₂Cl₂aliquots were combined and washed with two, 125 mL aliquots of deionizedwater and one 125 mL aliquot of brine. The CH₂Cl₂ fraction was driedwith MgSO₄, filtered, and the solvent then removed under reducedpressure to yield 5.33 g of crude product as a waxy yellow solid (65%yield). The bis-crown was recrystallized from heptane, washed twice withhot methanol, and dried under reduced pressure.

FIGS. 6A and 6B show ¹H NMR and ¹³C NMR spectra for bis-crown. ¹H and¹³C NMR spectra were collected on a Bruker AC 300 MHz spectrometer inCDCl₃ and spectra were referenced to the residual solvent peaks (¹H, δ7.27; ¹³C, δ 77.16). FIG. 6A shows the ¹H NMR spectrum for bis-crownusing the method described above to make the bis-crown. The ¹H NMRspectra for both bis-crown and crown acid (FIG. 5A) display aromaticproton peaks with the same splitting pattern, matching peaks for crownether ring protons, and similar peaks in the aliphatic region, with theexception of the triplet at 2.34 ppm. The protons represented by thistriplet are analogous to those observed at 2.90 ppm in the bis-crownspectrum due to the symmetry in bis-crown.

FIG. 6B shows the ¹³C NMR spectrum results for the bis-crown that wasproduced using the above method. The ¹³C NMR spectrum showed the numberof carbon peaks is reduced from 26 for the crown acid (FIG. 5B) to 20for the bis-crown due to the symmetry of the molecule. Furthermore, thepeak at 178 ppm representing the carboxylic acid carbon observed in thecrown acid spectrum is not present in the bis-crown spectrum due to theformation of a second ketone.

Example 3: Synthesis and Functionalization of Magnetite Nanoparticles

There are two examples of synthesizing and functionalizing the magnetiteparticles herein. First, the magnetitie particles are synthesized andfunctionalized in separate steps. In this example, FeCl₃.6H₂O (5 g, 18.5mmol) and FeCl₂.4H₂O (1.84 g, 925 mmol) were dissolved in deionizedwater (300 mL) and sparged with nitrogen for 2 hours. A 12 mL aliquot of14M NH₄OH was added dropwise over 30 min to produce fine black particlesof Fe₃O₄. The mixture was allowed to react for 2 hours using a stream ofnitrogen gas to mix the solution. The reaction mixture was then dividedamong six 50 mL tubes, which were centrifuged at 5000 rpm for 0.15minutes. After 15 minutes the supernatant liquid was decanted. 40 mL ofwater was added to each tube. The tubes were then shaken vigorously tobreak up the nanoparticle pellets, and the nanoparticles were isolatedusing centrifugation followed by decantation. This same process wasrepeated with acetone. The remaining solid was then dried under vacuumand collected. A quantitative yield of magnetite was obtained.

Next, magnetite nanoparticles (100 mg) were dispersed in 20 mL ofacetone containing 20 mg of dissolved crown acid and sonicated for onehour. Afterwards, the nanoparticles were magnetically separated and theremaining liquid was decanted. A 20 mL aliquot of fresh acetone wasadded to the magnetite nanoparticles and sonicated for 20 minutes. Thenanoparticles were magnetically separated from solution and dried underreduced pressure overnight to obtain functionalized magnetitenanoparticles.

In another example, the functionalized magnetite nanoparticles wereformed in-situ in a single step. FeCl₃.O₆H₂O (2.5 g, 9.25 mmol), andFeCl₂.4H₂O (0.92 g, 4.63 mmol) were dissolved in deionized water (300mL). Crown acid (100 mg) was added to the solution, which was thensparged with a stream of nitrogen gas for 2 hours. A 6 mL aliquot of 14M NH₄OH was added dropwise over 45 minutes, which produced fine blackparticles of Fe₃O₄. A stream of nitrogen gas was used to stir themixture for an additional 2 hours. The reaction mixture was then dividedamong six 50 mL tubes, which were centrifuged at 5000 rpm for 20minutes. After 20 minutes, the supernatant liquid was decanted. 40 mL ofdeionized water was then added to each tube. The mixtures were sonicatedfor 30 minutes, centrifuged at 5000 rpm for 20 minutes, and decanted.This process was repeated with acetone and the remaining solid was driedunder reduced pressure and collected to obtain the in-situfunctionalized magnetite nanoparticles.

FIG. 7 shows powder X-ray diffraction patterns from magnetite purchasedfrom Sigma Aldrich, synthesized magnetite that had not beenfunctionalized, and in-situ functionalized magnetite. The X-raydiffraction was performed to determine the average particle size. X-raydiffraction (XRD) patterns were collected on a Panalytical)(Pert ProX-Ray Diffractometer equipped with Ni-filtered Cu Kα radiation (λ=1.5418Å) and operated at 45 kV and 40 mA. The diffractograms were recorded inthe range of 4 to 70° (2θ) at a rate of 1.2 degrees/min.

In FIG. 7, the library diffraction pattern consists of nine lines at18.3°, 30.1°, 35.5°, 37.2°, 43:2°, 53.4°, 56.9°, 62.5°, and 65:7° (2θ).A comparison of the three sample patterns to that of the libraryspectrum reveals that these characteristic lines are present at the samerelative intensity, confirming the identity of each sample as magnetite.The peaks observed in the diffractograms of both the synthesizedmagnetite and in situ functionalized magnetite exhibit a broadening thatis indicative of a smaller particle size compared to that of the SigmaAldrich reference sample (50 nm to 100 nm). The average particle size ofthese two samples was calculated as a function of the peak broadeningusing the Scherrer Method. The average particle size of the synthesizedmagnetite and the in situ functionalized magnetite was determined to be20.4 nm and 24.0 nm, respectively.

FIGS. 8A-8B and FIG. 9 show Fourier-transform infrared spectroscopy(FTIR) results of bis-crown, crown acid, and in-situ functionalizedmagnetite, respectively. The infrared spectrometry was performed usingan Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR)spectrometer with a single bounce diamond ATR crystal. The instrumentused was a Nexus 870 FTIR spectrometer with a liquid N2 cooled mercurycadmium telluride (MCTA) detector.

In FIG. 8A, the carbonyl peak in the spectrum of the bis-crown has beenshifted to 1671 cm⁻¹, consistent with ketone formation. In contrast, inFIG. 8B, the crown acid spectrum exhibits two absorption peaks at 1730cm⁻¹ and 1674 cm⁻¹, representing the carboxylic acid carbonyl and theketone carbonyl, respectively. In FIG. 9, the in-situ functionalizedmagnetite nanoparticle spectrum exhibits a much less intense carbonylstretching peak at 1735 cm⁻¹ and a higher intensity carbonyl stretch at1672 cm⁻¹. These are the same peaks identified for the crown acid, butthe lower intensity of the peak at 1735 cm⁻¹ indicates that most of thecarboxylic acid functionalities are now present as carboxylate groups.The carboxylate stretch, typically between 1639-1646 cm⁻¹, is not seendue to the overlap of other peaks. The peak at 1735 cm⁻¹ suggests thatsome of the ligand exists as the carboxylic acid and may be bound to thenanoparticle by either hydrogen bonding or dipole forces between thehydrophobic segments of the ligands.

FIG. 10A-10B shows the thermograms from using thermogravimetric analysis(TGA) of post-functionalized crown acid magnetite nanoparticles andin-situ functionalized crown acid magnetite nanoparticles, respectively.TGA was performed to determine the degree of nanoparticlefunctionalization by the crown acid. TGA was performed on a TAInstruments Q5000IR TGA under a nitrogen flow of 50 mL/min using atemperature profile starting at 30° C. and increasing to 500° C. at 5°C./min.

In both FIGS. 10A and 10B, the crown acid loses 96.2% of its mass viathree steps due to volatilization and thermal decomposition of thesample. The initial mass loss begins at 188° C. The TGA of thepost-modified magnetite nanoparticles shows a mass loss of 5.95% with anonset temperature of 230° C. The higher temperature is attributed to thechemical bonding between the ligand and the nanoparticle surface.Similarly, the in situ treated magnetite nanoparticles lose 5.58% oftheir mass with an onset temperature of 208° C. The curve for the insitu treated magnetite nanoparticles is much flatter than thepost-modified magnetite nanoparticles, suggesting that the ligands maybe bound to a wider variety of surface sites compared to the ligands inthe post-modified magnetite nanoparticles.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint. The degree offlexibility of this term can be dictated by the particular variable andwould be within the knowledge of those skilled in the art to determinebased on experience and the associated description herein.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Unless otherwise stated, any feature described herein can be combinedwith any aspect or any other feature described herein.

Reference throughout the specification to “one example”, “anotherexample”, “an example”, and so forth, means that a particular element(e.g., feature, structure, and/or characteristic) described inconnection with the example is included in at least one exampledescribed herein, and may or may not be present in other examples. Inaddition, it is to be understood that the described elements for anyexample may be combined in any suitable manner in the various examplesunless the context clearly dictates otherwise.

It is to be understood that the ranges provided herein include thestated range and any value or sub-range within the stated range. Forexample, a range from about 1 nm to about 100 nm should be interpretedto include not only the explicitly recited limits of from about 10 nm toabout 65 nm, but also to include individual values, such as 3 nm, 37 nm,50 nm, etc., and sub-ranges, such as from about 25 nm to about 55 nm,etc.

In describing and claiming the examples disclosed herein, the singularforms “a”, “an”, and “the” include plural referents unless the contextclearly dictates otherwise.

What is claimed is:
 1. A method for removing ionic contaminants,comprising: mixing crown ether functionalized substrates with mediacontaining ionic contaminants, thereby binding the ionic contaminants tothe crown ether functionalized substrates; separating the crown etherfunctionalized substrates from the media; and regenerating the crownether functionalized substrates, thereby releasing the ioniccontaminants from the crown ether functionalized substrates.
 2. Themethod of claim 1, wherein the crown ether functionalized substrates areparticles that are mixed with the media by shaking, stirring,sonication, dynamic flow, or combinations thereof.
 3. The method ofclaim 1, wherein the crown ether functionalized substrates are magneticor superparamagnetic particles.
 4. The method of claim 3, whereinseparating the magnetic particles includes using a magnetic field. 5.The method of claim 1, wherein separating the crown ether functionalizedsubstrates includes removing the media from the mixing chamber orfiltering the media through solid supports.
 6. The method of claim 1,wherein regenerating the crown ether functionalized substrates includeschemical reduction or oxidation, electrochemical reduction or oxidation,exchange reactions, solvent washing, or combinations thereof.